Articles & Case Studies

Reduced carbon footprint from UU’s first containerised dosing system

Posted: Friday 20th June 2008

The first containerised or packaged dosing system to be deployed by United Utilities has been commissioned to carry out phosphate removal as part of the major upgrade at the Fazakerley WwTW site in Liverpool. Supplied by Gee & Company, the factory-produced package has been chosen because of the benefits it will deliver compared with a traditionally-built dosing system, notably cost and time saving, and reducing the carbon footprint of the site.

Upgrading of this established plant, which has a dry weather flow of 39,564 m³/day, is being carried out for UU by the Galliford, Costain Atkins (GCA) joint venture. The new containerised dosing system will store and dose ferric chloride or ferric sulphate to provide state-of-the-art phosphate removal. It is comprised of three units, two of which are for chemical storage-only, with the third being a combined storage and dosing module. All three are hydraulically linked, giving a total storage capacity of 144 cubic metres, which represents fourteen days’ storage at maximum dosing rates or, more typically, up to thirty days at anticipated dosing rates.

United Utilities says that a team decision to adopt the containerised solution was taken in consultation with the GCA joint venture. Apart from a significant cost-saving compared with traditional methods of construction, among the predicted benefits were a significantly reduced site installation and commissioning time, together with a much reduced requirement for associated civil work. The packaged units supplied by Gee require only a pre-laid concrete slab and associated dosing lines and electrical hook-up.

Additionally, because they are fabricated, assembled, tested and pre-commissioned with in the more easily controlled environment of a factory, they can be brought on-line within days of delivery to site.

Taking a long-term view, UU was also aware that if the site requirement should ever change, the units could be used to dose other chemicals or even moved to another site. Moreover, at the eventual end of the asset life, the containers can be removed for recycling. Significantly, all this helps to reduce the overall carbon footprint at Fazakerley.

Each of the two storage containers houses twin 24 cubic metre capacity fully bunded chemical storage tanks, constructed of Celmar GRP and built to the requirements of BS 4994, Cat 1. The configuration allows them to be used either jointly for chemical storage or independently for duty/standby purposes.

Apart from housing twin tanks, the storage/dosing container incorporates twin Signal Series 300 LY pumps. For safety, they incorporate double diaphragms, with visual diaphragm rupture detection, incorporating Signal’s latest ‘smart’ diaphragm technology. These pumps, which are some of the largest of their type ever supplied by Gee in a packaged system, are housed within polypropylene skids and provide a duty/standby function. Their output is controlled by a servomotor, which doses in proportion to works flow by adjusting the stroke length automatically.

Also housed within the container – but within a separate, dedicated area – is the electrical control room, featuring a Form 4 MCC fitted with a Siemens PLC and HMI.

Twin injection points dose ferric to the humus tank and the BAFF plant respectively, using double-contained connecting dosing lines. With operational safety being a prime driver throughout the system, these lines are double-contained. A catch pot incorporating level sensors is installed at every low point ensuring that, in the event of a leak, chemical would run back to the catch point, and the leak detected, enabling the plant to be turned off.

The packaged approach developed by Gee & Company is applicable to a wide range of dosing capacities, extending from 3 cubic metres up to 200 cubic metres

Apart from the new phosphate removal system, the scope of the GCA contract includes the provision of centrifuges thickening works sludge. GCA also provided auto de-sludging on both the primary and the humus tanks, which will enable the system to handle increased sludge make together with the higher dry solids content of this sludge.

Tel: 0121 326 1700.

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